The present invention relates to permanent magnet couplers of the type having a magnet rotor on one shaft adjustably spaced from a conductor rotor on another shaft. More particularly, the invention relates to mounting the adjustable rotor to its respective shaft.
Induction motors are used, for example, to drive fans, blowers, pumps and compressors. It has been recognized that when these motors are operated at full speed they normally have excess capacity as compared to the load requirements, and this excess capacity is compounded when the load is variable. It has also been recognized that if the output of the motors could be adjusted to provide only the needed power, a significant reduction of energy usage would result. Hence, variable speed drives (VSD""s) have been developed in the form of electronic devices which match motor speed to that required for a given application. A typical VSD rectifies incoming AC voltage and current into DC, then inverts the DC back to AC at a different voltage and frequency. The output voltage and frequency is determined by the actual power needs and is set automatically by a control system or by an operator.
Heretofore, VSD""s have generally been so expensive that they have not been used extensively for energy savings. It has been reported that VSD""s require the availability of highly trained maintenance personnel and shorten motor life.
U.S. Pat. No. 5,477,094 (the ""094 patent) shows a magnetic coupler in which a magnet rotor unit is straddled by two conductor rotors which are connected together to rotate as a conductor rotor unit on one shaft while the magnet rotor unit is mounted to rotate on a second shaft. The magnet rotor unit has a set of permanent magnets arranged with their opposite poles spaced by air gaps from ferrous-backed electroconductive rings mounted on the respective conductor rotors. Rotation of one of the two shafts results in rotation of the other shaft by magnetic action without there being any direct mechanical connection between the shafts.
The ""094 patent also discloses the concept of having two magnet rotors rather than a single magnet rotor unit, with each magnet rotor having a respective set of permanent magnets spaced by an air gap from one of the electroconductive elements presented by the conductor rotors. The two magnet rotors are axially moveable relative to one another and are spring biased apart.
In U.S. Pat. No. 6,005,317 (the ""317 patent), the magnet rotors are positively positioned relative to each other such as to vary their axial positions automatically at will from a remote control location to provide by air gap adjustment a variable torque from a constant speed motor to a variable torque load operating at a lower constantly maintained speed.
Instead of spring biasing the two magnet rotors as in the ""094 patent, the positions of the magnet rotors in the ""317 patent are controlled from a stationary control mechanism which communicates with an adjusting mechanism operating on the magnet rotors to selectively move them toward one another to widen the air gaps or to move them further apart to narrow the air gaps. Gap adjustment varies the rotational slip between the magnet rotor units and the conductor rotor units for a given torque load and hence affects the speed of the load. For a given torque load the air gaps can be adjusted to provide the torque at a preset rotational speed differential below the speed of the motor.
The present invention is directed toward adjustable magnetic couplers in which a magnet rotor and a conductor rotor are positioned in proximity with each other such that rotation of one rotor results in rotation of the other. A hub is engaged with a first shaft, and is configured to slide with respect to the first shaft but not rotate with respect to the first shaft. Consequently, as the first shaft rotates, the hub rotates with it. The magnet rotor is coupled to the hub and the conductor rotor is coupled to a second shaft, or vice versa. The rotors are configured to rotate with the respective shaft. A push-pull mechanism is rotatably coupled to the hub such that the push-pull mechanism maintains stationary even when the first shaft and the hub rotate. The push-pull mechanism is operative to move the hub and the rotor attached thereto axially along the first rotary shaft. Axial movement of one rotor with respect to the other rotor changes the distance between the magnet rotor and the conductor rotor, altering the performance of the coupler.
In another embodiment of the present invention, a pair of adjustable rotors are spaced from a fixed rotor assembly, and are adjustable through the use of a push-pull mechanism similar to that discussed above. A first adjustable rotor is linked to the second adjustable rotor such that movement of one rotor results in movement of the other. In one particular embodiment, movement of the hub and the first adjustable rotor in one direction results in a corresponding movement of the second adjustable rotor in an opposite direction. Accordingly, movement of the first adjustable rotor results in an adjustment of the spacing between both adjustable rotors and a third, fixed rotor. As the adjustable rotors are configured with magnets and the fixed rotor configured with an electroconductive ring, or vice versa, adjustment of the spacing between the three rotors results in an adjustment to the performance of the system.
In yet another embodiment of the present invention, the adjustable magnetic coupler comprises two fixed rotors and two adjustable rotors. The fixed rotors are coupled to a shaft to rotate with the shaft, but are not permitted to move axially along the shaft. The adjustable rotors, on the other hand, are movable in an axial direction with respect to the shaft, but are not permitted to rotate with respect to the shaft. One of the adjustable rotors is mounted on a slidable hub. The adjustable rotors are linked together such that axial movement of one adjustable rotor results in a corresponding axial movement of the other adjustable rotor. Consequently, adjustment by a push-pull mechanism of the hub and one adjustable rotor results in a corresponding adjustment of the other adjustable rotor. Using the push-pull mechanism, the first and second adjustable rotors can be spaced by a desired distance from the respective first and second fixed rotors, modifying the performance of the magnetic coupler system.